The present invention relates to a friction winding shaft, and, in particular to a winding shaft for roll cutting and winding machines.
Roll cutting and winding machines in which wide webs are pulled from a supply roll and are then divided into strip-shaped bands are known (German DE-OS 28 56 066). The bands are wound up on tubular cores which are placed on a friction winding shaft. To wind up the strip-shaped bands, two friction winding shafts are provided at a distance from each other so that every other strip-shaped band is wound up on one friction shaft and the strip-shaped bands in between are wound up on the second friction winding shaft.
As the strip-shaped bands are wound up, different winding diameters are produced due to differences in the thickness of the material web, so that the winding cores placed on a friction winding shaft can no longer be driven at the same rotational speeds. The drive shaft is therefore driven at a somewhat higher rotational speed than is required to wind up the strip-shaped bands. The rings placed on the drive shaft are slaved by the friction contact between the inner ring surfaces and the friction surfaces on the pressure elements, but they tend to slip slightly to compensate for the difference between the rotational drive speed and the rotational winding speed. The force of friction contact can be altered by changing the pressure in one of the inflatable hoses placed under the pressure elements.
The pressure elements are in this cases made in form of three pressure strips extending in the longitudinal sense of the drive shaft and are designed so that they can adapt, at least in the longitudinal sense, to different inside diameters of adjoining rings.
The entire effective length of the drive shaft is taken up by narrow rings immediately adjoining each other. This results in identical winding tensions in all the bands of the friction winding shaft to be wound up since each pressure strip is applied with an identical contact pressure to each inside ring surface.
The rings serving to hold the winding cores are provided with elastic projections on the outer ring surface. In particular, sheet metal springs are provided which are oriented at a slight angle relative to the radius in the direction of drive. The springs are pressed against the inside surfaces of the winding cores and function as a spring tension. As the bands are wound up, the free, edge-shaped ends of the projections press slightly into the material of the winding cores and thus constitute a slip-free connection with a winding core.
In addition, another embodiment of winding core retainers is known on the market in form of spring-loaded rotating parts used as clamping elements with projecting contact edges across from the outer holder surface. These roof-shaped contact edges are also at a slight angle to the radius in the direction of drive, and are pressed against the inside winding core surface and function as spring tension.
To remove the wound-up winding cores they are rotated in driving direction relative to the stopped rings. This is possible because this rotation is in the sense of winding core retainer slant. Rotation in this direction and lateral shifting make it possible to remove the winding cores together with the wound-up bands from the friction shaft and to install new winding cores.
The winding cores are normally made of a paper material or a plastic with relatively wide tolerances. The diameter tolerances of the inside core diameter of the winding cores are taken up by the available elastic movement of the winding core retainers, so that this available elastic movement must be sufficient.
Because of this elastically supported freedom of movement of the winding cores in relation to the rings which is necessary because of the winding core tolerances, centering and perpendicular alignment of the winding cores in relation to the drive shaft is not sufficiently precise in certain instances of application. These minor deviations may result in a upward leap and/or in minor wobbling movement which, however small, may nevertheless lead to unsatisfactory winding results under certain circumstances. A similar winding shaft is known (German DE 39 18 863 A1) where the friction rings are provided with slanted guides for the support of winding cores. The slanted guide is designed so that the winding core supports can be moved within the diameter tolerances of the cores.
Accordingly, an object of the present invention is to provide a friction winding shaft having improved centering and alignment of the installed winding cores to prevent upward leaps and wobbling of the winding cores.